The present invention relates generally to object tracking and management systems and methods, and more specifically to such systems and methods that use a combination of mobile and/or stationary radio-frequency identification tags to identify, monitor the locations of, and direct movements of objects.
To achieve highly efficient warehouse operations, it is desirable to accurately track the movements of pallet loads and other objects to be located and/or transferred within the warehouse as they are transported to and from various locations, such as storage locations, stocking locations, staging areas and loading docks. In typical conventional warehouse management operations, the operator of a transport vehicle, such as a fork truck, reach truck, lift truck or pallet truck, receives a set of printed stocking or picking orders, typically generated by a computer, and executes the orders by visually identifying the loads and locations and transporting the loads to and from the locations specified on the orders. In such a system, especially in large-scale warehouses with a large number of locations and loads to handle, there are numerous opportunities for errors.
Some warehouse management operations use bar codes which are affixed to the loads or which mark specific locations. In a typical example of such a system, the operator uses a hand-held bar code scanner to read the bar code on the loads and, in some cases, on the stock locations. Although such a system is an improvement over purely visual processes, it can be difficult to completely implement, due partly to the need for direct line of sight, close proximity, and proper alignment between the scanner and barcodes. It also requires the operator to participate in the load-identification process. In some case, the operator may need to exit the transport vehicle to scan the barcodes manually, slowing down warehouse operations. Certain locations, for example high storage shelves and loading docks, often are particularly difficult places for using bar codes because of the need for close proximity between the codes and the reader. As a result, loads in those areas are often visually identified instead.
Radio-frequency identification (xe2x80x9cRFIDxe2x80x9d) tag systems have been proposed for use in inventory tracking. In such a system, an RFID tag is attached to an object or location, and contains a non-volatile memory for storing information identifying the object or location and electronic circuitry for interacting with an interrogator. RFID tags may be passive or active. In the case of a passive RFID tag, the tag includes circuitry for converting at least a portion of the received RF signals into electrical power needed by the tag for signal processing and transmission. In a typical conventional system, RFID tags containing information associated with the identities of inventory items to be tracked are attached to the inventory items. An RFID interrogator is used to detect the presence of an RFID tag and read the identification information from the tag. A typical RFID interrogator includes an RF transceiver for transmitting interrogation signals to and receiving response signals from RFID tags, one or more antennae connected to the transceiver, and associated decoders and encoders for reading and writing the encoded information in the received and transmitted RF signals, respectively. The interrogator may be a portable device, which can be brought near the tags to be read, or it may be a stationary device, which reads the tags as they are brought to the interrogator, as in the case of tagged library books being returned to a return station that is fitted with an interrogator. RFID tags may also be affixed near a location as a location marker. After detecting both a tag attached to an inventory item and a location marking tag, a processing unit associated with the interrogator may determine that the inventory item is positioned near the tagged location. While these conventional object tracking systems are capable of keeping a record of the inventory items and sometimes their locations, they are not effective for tracking and/or managing the movement of the inventory items.
There also exist warehouse inventory tracking systems that include fixed RFID interrogators at various locations to detect RFID-tagged items when they are positioned near the interrogator-equipped locations. For example, there are warehouses with RFID interrogators positioned at or near the loading dock gates. Such systems are capable of tracking the arrival of tagged items at the various locations, but are not capable of detecting errors remote to these locations. For example, if a fork truck picked up a wrong load because the truck was driven to a wrong pick-up location, the error would not be detected until the load had reached the gate. This delayed error detection negatively impacts the overall efficiency of warehouse operations. Additionally, outfitting each of the numerous loading dock gates with an interrogator is not cost effective.
It is desirable to provide a system that provides full automation to the process of object identification, movement and tracking throughout a warehouse or other similar environment. There is a need for such a system that is adaptable for use with all of the wide variety of locations that are involved in warehouse operations, such as stocking locations, storage racks, floor lanes, and shipping docks. There is a need for such a system that operates in conjunction with a central data repository to direct and track all object movement throughout the entire warehouse.
The present invention is directed to alleviating one or more of the aforementioned problems, and meeting one or more of the above-identified needs.
The invention provides for an automated object and location identification system, preferably for use in warehouse management operations, without the need to outfit numerous locations with fixed RFID interrogators. In one embodiment of the invention, a transport vehicle, such as a fork truck or reach truck, has mounted thereon an RFID interrogator. RFID tags are attached to objects (such as pallets and loads) and to locations (such as a storage location, pass-through location, or loading dock). In the case of a pallet, the information transmitted from the tag may include the identity of the pallet, the weight of the pallet, and an identification of the items on the pallet. In the case of a location, the information is indicative of the location, such as a location code or coordinates. The RFID interrogator transmits interrogation signals to the RFID tags. Each of the RFID tags transmits a signal encoded with the information particular to the tag in response to the interrogation signals when the vehicle is sufficiently close to the tag, though not necessarily within a direct line of sight.
A processor is operatively linked to the RFID interrogator for processing the signal received from the tags by the interrogator and determining the identity of the load and position of the detected location RFID tag. The processor may be located on board the vehicle, at a remote site, or at a combination of both.
RFID tags are preferably used on both the objects and the locations. Alternatively, an identification marker such as a barcode tag may be attached to the objects, while RFID tags are used at one or more locations. In this case, the interrogator on the transport vehicle also includes a barcode scanner for reading information stored in the barcode tags. Similarly, RFID tags may be used on the objects, while barcode tags are used at locations, such as alongside a loading dock door.
Preferably, the processor provides the operator with feedback information through a user interface on the identity of the object, the location where the object is positioned and the location to which the object is to be moved. For example, the processor may transmit an audible signal (such as a beep) or a visual signal (such as red or green lights or graphical display on a monitor) to the operator to inform the operator whether the correct object has been picked up or whether the object has been positioned at the correct location. The processor may further be configured to send instructions to the operator on the tasks to be performed.
The interrogator may also be instructed by the processor to send information, such as the movement history of an object, to the RFID tag on the object. The RFID tag stores the information, which may be subsequently read, for example, by an RFID interrogator at another site. Similarly, the interrogator may be instructed by the processor to send information to the RFID tag at a location, which is then stored by the location tag.
In another embodiment of the invention, the interrogator is capable of identifying, and thus reading information only from, the tag that is the closest in distance to the interrogator. This is accomplished by dynamically reducing the power in the interrogation signal until only the RFID tag closest to the interrogator responds. The probability of incorrectly identifying a location or object is thereby reduced.
In this embodiment of the invention, the processor may generate a signal, perceptible by the operator, which is indicative of the minimum interrogation signal strength required to detect the RFID tag being sought by the interrogator (the target RFID tag). The minimum interrogator signal strength may be represented as a confidence level (the lower the minimum signal strength, the higher the confidence level) or as an approximate distance between the tag and the interrogator (the lower the minimum signal strength, the shorter the distance.)
In another embodiment of the invention, a pass-through location, such a loading dock gate or a truck docked at the loading dock gate, is marked by an RFID assembly having two RFID tags spaced in close proximity to each other. An RF shield, such as a metal plate or metal screen, is positioned between the two tags. When the interrogator is on one side of the shield, only the tag that is on the same side of the shield as the interrogator responds to the interrogation signals. This arrangement thus enables the system to determine the direction of movement of an object relative to the pass-through location. For example, the system is able to determine whether the vehicle carrying the object has moved through the gate from inside the warehouse to the loading dock or from the loading dock into the warehouse.
In another embodiment of the invention, the transport vehicle is equipped with an RFID interrogator for object identification and optionally for location identification. Objects, and possibly locations, are marked with RFID tags. In addition, the warehouse floor is equipped with magnetic tape segments that provide magnetic signals indicative of the locations of the segments. The vehicle is additionally equipped with a magnetic signal reader for detecting the magnetic signals from the tape. The processor onboard the vehicle is operatively connected to both the RFID interrogator and the magnetic signal reader for determining the identities of the objects and optionally locations from the signals received from the interrogator and locations from the signals from the tape reader.
In another embodiment of the invention, the transport vehicle is of a xe2x80x9creach truckxe2x80x9d type, equipped with a lift mechanism capable of positioning an object at a plurality of heights. The vehicle is further equipped with a height sensor linked to the lift mechanism for generating a signal indicative of the height that the object is positioned by the lift. The signal indicative of the height could be electrical, visual, audible, magnetic, electromagnetic or another type of signal. This embodiment of the invention is particularly useful when loading or unloading objects from a vertical column of warehouse slots. In this embodiment, it is necessary to associate only a single location tag with the column, and the system can identify the correct slot within the column using the height sensor.
Thus, in one aspect of the invention, a system for tracking an object positionable at a plurality of locations includes: (a) a transport vehicle to move the object to and from any one of the plurality of locations; (b) an object marker associated with the object which stores information indicative of the identity of the object; (c) a plurality of location markers, each of which is positioned at one of the plurality of locations and stores information indicative of the location of the marker; (d) an interrogator, including a radio frequency transmitter and receiver, mounted on the transport vehicle to receive from the object marker the information indicative of the identity of the object and from the location markers the information indicative of the location of the markers; and (e) a processor, operatively connected to the interrogator. The processer determines the identity of the object from the information indicative of the identity of the object, the location of at least one of the location markers from the information indicative of the location of the marker and the spatial relationship between the object and the location. For example, the simplest form of such determination of spatial relationship is to determine that the object is located near or at a tagged location when the RFID tags of the object and the location are detected at substantially the same time.
The processor is also preferably capable of providing instructions to the operator through a user interface regarding movement of the objects. These instructions may include (a) feedback as to whether a desired object has been identified; (b) directions to a desired location; and (c) feedback as to whether the object has been brought to a desired location.
In the system above, the transmitter of the interrogator preferably is capable of transmitting a signal encoded with information, such as the movement history of the object or the storage history of the location, and the object or location marker stores the encoded information.
The system also preferably includes a signal generator operatively connected to the processor to provide to the operator of the vehicle a signal through a user interface, such as an audible beep or visual display of lights or computer monitor display, indicative of the location of one of the plurality of location markers when the interrogator receives from the location marker the information indicative of the location of the marker.
In another aspect of the invention, the RFID interrogator is configured and arranged to read information only from the RFID tag closest to the interrogator. This is preferably accomplished by dynamically reducing the output power of the interrogation signals until only the RFID tag the closest to the interrogator responds to the interrogation signals. A target confidence indicator is preferably included to provide visual feedback of the tracking process.
In another aspect of the invention, at least one of the location markers defines a plane, and the marker transmits a first signal indicating that the interrogator is located on one side of the plane and transmits a second signal, different from the first signal, indicating that the interrogator is located on the other side of the plane. The location marker may include two RFID tags separated by a shield, such as a metal plate or screen positioned generally in the plane, wherein only the RFID tag positioned on the same side of the plane as the interrogator responds to the interrogation signals from the interrogator.
Another aspect of the invention is a system for tracking an object positionable at a plurality of locations on a traffic-bearing surface. The system includes a transport vehicle to move the object between locations, an object marker associated with the object which stores information indicative of the identity of the object, and an interrogator mounted on the vehicle to receive from the object marker the information indicative of the identity of the object. The system further includes a strip of magnetic tape adhered to the traffic-bearing surface. The magnetic tape includes a plurality of segments. Each of the segments is encoded with information indicative of the location of the segments, and produces a magnetic signal encoded with the information indicative of the location of the segment. A magnetic signal reader is mounted on the vehicle for sensing the signals generated by the magnetic tape. A processor operatively connected to the interrogator and the magnetic signal reader determines the identity of the object from the information indicative of the identity of the object, the location of at least one of the segments of the magnetic tape and the spatial relationship between the object and the location.
Another aspect of the invention is a transport vehicle for moving an object having a radio-frequency identification tag attached thereon to or from locations at a particular height. The vehicle includes: (a) a radio-frequency identification interrogator to receive a signal from the tag; (b) a lift capable of positioning the object at a plurality of heights; (c) a height sensor to generate a signal indicative of the height at which the object is positioned; (d) means for generating a signal indicative of the horizontal location of the vehicle; and (e) a processor operatively connected to the interrogator, height sensor and signal generating means. The processor determines the identity of the object from the signal received from the tag, determines the height of the object from the signal received from the height sensor, and determines the horizontal location of the vehicle from the signal generating means.
Another aspect of the invention is a method of managing an object to be moved between locations in an environment. A first RFID tag is affixed to the object and has stored therein and capable of transmitting signals encoded with information indicative of the identity of the object. A second RFID tag is affixed at a location and has stored therein and capable of transmitting signals encoded with information indicative of the location of the second tag. A transport vehicle is equipped with an RFID interrogator, capable of receiving the signals from the tags and determining the information stored in a tag. The method includes the steps of: (a) using the interrogator to receive the information indicative of the identity of the object; (b) determining a proposed location to which the object is to be moved; (c) using the vehicle to move the object to a location; (d) using the interrogator to receive the information indicative of the location; and (e) depositing the object at the location when the location indicated by the information received in step (d) matches the proposed location.
Another aspect of the present invention is a method of using an RFID interrogator with an adjustable power output level to find a target RFID tag among a plurality of radio-frequency identification tags. Each of tags is configured and arranged to transmit an identification signal in response to an interrogation signal from the interrogator. The method includes the sequential steps of: (a) transmitting interrogation signals at a power output level; (b) determining whether the target tag has been detected by the interrogator; (c) reducing the power output level if the target tag is detected; (d) repeating steps (a)-(c), each time using the power output level reached at step (c) of the previous repetition as the power output level in step (a) until the target tag is no longer detected; and (e) transmitting an interrogation signal at the power output level reached at the end of repetition immediately previous to the last repetition in (d).